Scenario: a nameserver is misconfigured such that it doesn't set the "recursion available" (ra) bit on its replies. Postfix's relayhost has an A record but no MX record, and is specified in main.cf without [] brackets around it.
What I see is that Postfix 2.6.6 looks up the MX record, receives a successful negative reply (but with the ra bit unset), and defers with "Host or domain name not found. Name service error for name=[REDACTED] type=MX: Host not found, try again". RFC 5321 section 5.1: The lookup first attempts to locate an MX record associated with the name. If a CNAME record is found, the resulting name is processed as if it were the initial name. If a non-existent domain error is returned, this situation MUST be reported as an error. If a temporary error is returned, the message MUST be queued and retried later (see Section 4.5.4.1). Is a response with 'ra' unset an error? If not, then I'd expect Postfix to continue to the "implicit MX" behavior and look up the A record. If so, then I guess the observed behavior is correct. What do you think? Best regards, -- Ben Rosengart 2.3.2 418 I'm a teapot Any attempt to brew coffee with a teapot should result in the error code "418 I'm a teapot". The resulting entity body MAY be short and stout.
